Sensor

ABSTRACT

The present invention relates to sensor for indicating a cumulative time period of presence of an ambient relative humidity, there the sensor comprising an indicator and a carrier and the indicator being located at one or more limited portions of the carrier. The carrier allowing migrating of the indicator within the carrier and the indicator causing an extension thereof by migrating from the one or more limited portions when the ambient relative humidity level exceeds a predetermined level. Further, the extension by migrating being detectable by a user and the cumulative time period being related to the extension by migrating and the characteristics of the indicator and the carrier. The present invention also relates to a method for reading the cumulative time period of presence of an ambient relative humidity indicated by a sensor and a method for providing a sensor for indicating a cumulative time period of presence of an ambient relative humidity by providing a carrier with an indicator.

TECHNICAL FIELD OF THE INVENTION

This invention relates to a sensor for indicating a cumulative timeperiod of presence of an ambient relative humidity. The presentinvention also relates to a method for reading a cumulative time periodof presence of an ambient relative humidity indicated by a sensor and amethod for providing a sensor for indicating a cumulative time period ofpresence of an ambient relative humidity by providing a carrier with anindicator, wherein the indicator is arranged at one or more limitedportions of the carrier.

BACKGROUND OF THE INVENTION

Exposure to moisture can lead to undesired changes to a product duringmanufacture, storage, handling or transportation. Examples of moisturesensitive goods may be construction materials, food stuff,pharmaceuticals, boats, buildings, houses, vehicles, electronicequipment and so on. There are some known sensors in the prior art forindicating moisture.

U.S. Pat. No. 4,292,916 describes a timer and a storage conditionindicator comprising a carrier mixture and a receptive layer. In thisinvention a sensor shift is mainly triggered by parameters such astemperature, exceeding a set value.

U.S. Pat. No. 4,098,120 describes a sensor comprising at least anabsorbent wick. Herein, the indication of humidity is based on aphenomena called wick action and a course of time during which amaterial is exposed to moisture, is greatly depending on the amount ofavailable moisture.

Further, U.S. Pat. No. 4,793,180 describes an irreversible humidityindicator having a delayed response time including a porous plasticcarrier. However, the humidity level measured is the level inside hollowgoods using a complicated device shown in the document.

A disadvantage with the sensors in the prior art is that they preferablyindicate the exposure as such for predetermined levels of relativehumidity.

SUMMARY OF THE INVENTION

One object of the present invention is to achieve a sensor which is ableto indicate whether a product, an item, an object and/or a material hasbeen exposed to a certain amount of humidity preferably duringmanufacture, packaging, storage, transport and/or handling and toestimate for how long the product, item, object or material has beenexposed to a relative humidity that exceeds a predetermined humiditylevel. The predetermined humidity level is depending on the products,items, objects or materials sensitivity for humidity.

Another object of the invention is to achieve a sensor how isirreversible, impervious and stable.

According to a first aspect of the invention, the above and otherobjects are achieved with a sensor for indicating a cumulative timeperiod of presence of an ambient relative humidity there the sensorcomprises an indicator and a carrier. The indicator is located at one ormore limited portions of the carrier. The carrier allows migration ofthe indicator within the carrier and the indicator causes an extensionthereof by migrating from the one or more limited portions, when theambient relative humidity level exceeds a predetermined level. Further,the extension by migration is detectable by a user and the cumulativetime period is related to the extension by migration and thecharacteristics of the indicator and the carrier. This means that thecarrier allows the indicator to migrate within and/or at a surface layerof the carrier when a predetermined humidity level is exceeded andceases migration of the indicator when the ambient relative humiditylevel is lowered below said predetermined level and resuming migrationwhen the ambient relative humidity level again exceeds saidpredetermined level. An advantage of using a sensor according to theinvention compared to a sensor with a so called wick action usingcapillary rising is that it is possible to indicate a cumulative timeperiod of presence of an ambient relative humidity.

In addition, different kind of products, materials and objects are invarious degrees sensitive to moisture and according to the presentinvention it is possibility to design specific sensors, definingdifferent predetermined humidity levels, by using several carriersand/or indicators.

In a preferred embodiment of the present invention the carrier is atleast one of a hygroscopic material and a material that has been givenhygroscopic properties during preparation or modification. A hygroscopicmaterial is capable of adsorbing and desorbing moisture, respectively,i.e. water vapour and/or water, depending on the ambient relativehumidity of the surrounding atmosphere in such way that equilibrium isachieved. This enables manufacture and use of an irreversible sensor.

Another advantage of using a hygroscopic carrier is that the indicatorand the carrier is humid at approximately the same time and thereforecapillary rising is avoided. Be using the mentioned carrier theindicator is forced to diffuse through the carrier, i.e. resulting in adiffusion controlled or transport controlled process, which is a muchmore slowly process compared to a capillary rising process. Thetransport of different indicator substances is here controlled by theirabilities to migrate. For instance, water-soluble molecules are utilisedrequiring dissolution in a solvent to be able to move.

Further, the migration of an indicator according to the inventionpreferably occur through diffusion of the indicator or by transportationof the indicator molecules in the water phase, i.e. the indicatormolecules, such as a dye, is following the water through the sensor.Suitable materials for a carrier can for instance be paper, fabric andnon-woven materials. More preferable the carrier consists of at leastone of glass, glass fibre, polyester, polypropylen, cellulose, polymeretc.

In a preferred embodiment of the invention the hygroscopic material isat least one of an absorbent, a suitable porous material, a pore system,and a material with a rough or rugged surface. The main advantage ofutilizing a pore structure of a material is that the material can bedesigned to exhibit hygroscopic properties, due to the fact that thereis a significant relationship between the geometric structure of thepore system and the their ability to absorb water and moisture. Further,a porous system can also be monitored for temperature.

In another preferred embodiment of the present invention the pore systemis continuous.

In a preferred embodiment of the invention the sensor comprises anindicator and a carrier, where the carrier is an absorbent compoundcapable of absorbing water/water vapour from the surrounding air.According to this embodiment the indicator migrates through an absorbentin response to ambient humidity, i.e. when a predetermined relativehumidity level is exceeded and the migration of the indicator ceaseswhen the ambient relative humidity level is lowered below saidpredetermined level and also the migration is resumed when the relativehumidity level again exceeds said predetermined level.

In a preferred embodiment of the invention the carrier is provided withan absorbent.

In another preferred embodiment of the invention the absorbent is asalt, preferably a hygroscopic salt. Here the invention takes advantageof the relative humidity equilibrium of a saturated salt solution. Ahygroscopic salt stands in equilibrium with the moisture content of thesurrounding air. For many salts, the equilibrium follows lows therelative humidity. If the ambient air contains more moisture than theequilibrium relative humidity of the salt, the salt will absorb waterand alternatively, a humid salt will give away moisture at equilibriumrelative humidity. This phenomena is used to design a irreversiblesensor or a irreversible moisture indicator.

Further, this phenomena is utilized so that the salt dissolves into freewater, and thereby give rise to a colour change, or that the salt allowsto be absorbed into an absorbent according to the present invention.

In a more preferred embodiment of the invention the salt is at least oneof, or a combination of, NaCl, KCl, LiCl, LiBr, ZnBr₂, KOH, LiI,K₂C₂R₃OH, MgCl₂, NaI, K₂CO₃, Mg(NO₃)₂, NaBr, Kl, NaNO₃, KBr, (NH₄) ₂SO4,K₂NO₃ and K₂SO4. As hygroscopic active substance, inorganic salts arepreferable since they have a defined equilibrium relative humidity.

In a preferred embodiment of the invention the hygroscopic material isat least one of a hygroscopic thickening agent, a consistency agent anda gelation agent. Preferable, these agents are at least one of (or anycombination thereof) E400-E495 and E1404-E1451 (see table 1). The use ofa hygroscopic thickening agent or a hygroscopic composition as a carrierenables many new applications of the sensor according to the invention.One advantage using a hygroscopic thickening agent, composition ormixture is that the carrier directly can be printed on, sprayed on,painted on and/or coated on a surface of an item. Preferable, thementioned surface is modified, for example by hydrophobing, beforeprinting on, spraying, painting and/or coating the hygroscopicthickening agent, (composition or mixture) onto the surface of an itemin order to keep the accuracy of the sensor. Herein the term itemincludes almost everything having a surface being exposed to asurrounding, for instance a pill, a tablet, a paper, a plastic material,cellulose, a fibre, a label, a packing, a wrapping, a board and thelike. The item is exposed to a humidity at least one of the processes ofmanufacturing, printing, packing, wrapping, storing, transportation andhandling.

In a more preferred embodiment the hygroscopic thickening agent is oneof a gel compound, a gel matrix, gelatine and potato flour.

Further, the gel matrix comprises at least one of a hygroscopiccomponent and an indicator. Other components that may be included in thegel or gel matrix, in order to prevent transparency of the gel, is forexample TiO₂ which will be permeable for the indicator.

In a preferred embodiment of the invention the carrier further comprisesa hygroscopic thickening agent for keeping water in the carrier. This isparticularly important for sensors indicating a cumulative time periodof presence of an ambient relative humidity at lower levels of relativehumidity (RH).

In a preferred embodiment of the present invention asuitable porousmaterial has a continuous pore system and is at least one of a fibre,paper, wood, corrugated fibreboard, woven or non-woven materials andclay.

In a preferred embodiment of the invention the indicator is a colourindicator such as dye, pigment, hue and paint. A colour shift accordingto the invention is indicated in different ways.

In a preferred embodiment of the invention the carrier is arranged toallow migration of the indicator from the interior of the carrier to itssurface, allowing visual detection of a user.

In another preferred embodiment of the invention the carrier is arrangedto allow migration of the indicator at a surface layer of the carrier,also allowing visual detection of a user. It is possible for a sensoraccording to the present invention to at least change colour or useanother optical property as an indicator, for example a dye, migratingwithin a carrier of the sensor or along an observed surface layer of thecarrier. Preferably, the indicator, such as a dye, is water-soluble orpartly water-soluble. Some indicators requires free water to be able tomigrate. The indicator is preferable designed in order to preventmigration within a hygroscopic carrier and/or free salt-containingwater. It is not necessary for the indicator to react chemically withfor instance specific salts or the surface of a carrier. A clearer shiftis obtained by utilising chemical or physical bonding to the carrier orto an absorbent component. Further, suitable indicators may be chosenfrom ions, molecules, and polar organic molecules of a certain size andthe indicator can be in the form of a solution, suspension or emulsion.

In a preferred embodiment of the invention the indicator is a dye usedin the food industry. One advantage using dyes for the food industry isthat most of these dyes are non-toxic. Preferably, at least one of orany combination of E100 cur cumin, E101 riboflavin,riboflavin-5′-phosphate, E102 tartrazine EI04, quinoline yellow, E107yellow 7G, E110 sunset yellow FCF, orange yellow S FD&C Yellow No.6,E120 cochineal, carminic acid, carmines, E122 azorubine, carmoisine,E123 amaranth FD&C Red No.2, E124 ponceau 4R, cochineal Red A FD&C RedNo.4, E127 erythrosine FD&C Red No.3, E128 red 2G, E129 allura red ACFD&C Red No.40, E131 patent blue V, E132 indigotine, indigo carmine FD&CBlue No.2, E133 brilliant blue FCF FD&C Blue Dye No.1, E140chlorophylis, chlorophyllins, E141 copper complexes of chloropyll andchlorophyllins, E142 green S, E150(a) plain caramel dark brown colourmade from sucrose, E150(b) caustic sulphite caramel see E150(a), E150(c)ammonia caramel see E150(a), E150(d) sulphite ammonia caramel seeE150(a), E151 brilliant black BN, Black PN, E153 vegetable carbon, E154brown FK, E155 brown HT (chocolate), EI60(a) carotene, alpha-, beta-,gamma-, E160(b) annatto (arnatto, annato), bixin, norbixin, EI60(c)paprika extract, capsanthin, capsorubin, EI60(d) lycopene, EI60(e)beta-apo-8′-carotenal (C 30), EI60(f) ethyl ester ofbeta-apo-8′-carotenic acid (C 30), E161(b) xanthophylls-lutein, E161(g)xanthophylls-canthaxanthin, E162 beetroot red, betanin, E163anthocyanins, E170 calcium carbonate, E171 titanium dioxide, E172 ironoxides and hydroxides, E173 aluminium, E174 silver, E175 gold, E180latolrubine Bk and E181 tannic acid and tannins is used. Similarcompounds or analogues to the E-dyes above, sharing the same properties,may also be used as a indicator dye in the present invention.

In another preferred embodiment of the invention the sensor is designedin such a way that the importance of the durability of the colourindicator is decreased. In such an embodiment, the sensor comprises atleast one carrier and an indicator, wherein the colour of the indicatoris visible (detectable) before the sensor is exposed to the ambientsurroundings. If the ambient relative humidity level exceeds apredetermined level the indicator starts to migrate (or diffuse) fromone or more limited portions of the carrier. If the colour of theindicator disappears, the predetermined relative humidity level iswidely exceeded, and if the colour of the indicator is still there(visible) the sensor is unexposed. One advantage with this type ofsensor is that the sensor has a much longer length of life, even if thedye isn't stable in a salt or in an ambient environment.

In another embodiment of the invention the extension by migration of anindicator is related to a colour shift of a non-migrating indicatorlocated at one or more limited portions on the carrier. Preferably, thesensor allows transport or migration of e.g. a pH-alteration within orat a surface layer of the sensor, wherein a non-migrating indicatorchanges colour when the pH-value is varied.

A further object of the invention is to achieve a method for reading acumulative time period of presence of an ambient relative humidityindicated by a sensor and to achieve a method for providing a sensorcarrier with an indicator.

In a preferred embodiment of the invention a method for reading thecumulative time period of presence of an ambient relative humidityindicated by a sensor mentioned before comprises the steps of; a)observing the extension of the indicator having extended by migratingfrom one or more limited portions, when the ambient relative humiditylevel have exceeded a predetermined level, and b) establishing thecumulative time period of presence of an ambient relative humidity byrelating the extension of the indicator to a time period reference, isused. One advantage by using this method is that it enables anindication of for how long the ambient relative humidity level hasexceeded a predetermined humidity level. From that information a user isable to estimate the damage of the item being exposed to an ambientsurrounding.

In another preferred method of the invention a time period reference isused. Preferably, the time period reference is at least one of arrangedin relation to the carrier, a stand alone tool for physical alignment tothe extension of the carrier at the time of the measuring of theextension and a table comprising relations between extension and time.It is desirable to aim at and design a user-friendly time periodreference.

In a preferred method of the present invention an external light sourceis used to assist in the visual detection. Preferably, the light sourceis one of a infra red light source, an ultra violet light source and avisible monochromatic light source.

Further, the detection of the sensor can be a colour shift directlyvisible to the eye or a “hidden” colour shift, which may be visibleunder a source of for instance ultraviolet- or infrared light. It isalso possible that the indicator can be developed using chemical orphysical reactions in able to detect a shift. The indicator may alsogive rise to changed surface properties of the carrier, which preferablewill be visible for the naked eye.

In a preferred embodiment of the invention a method for providing asensor for indicating a cumulative time period of presence of an ambientrelative humidity is used by providing a carrier with an indicator,wherein the indicator is arranged at one or more limited portions of thecarrier. This gives a good flexibility. Preferably, the indicator may bearranged within the carrier and/or directly on the surface layer of thecarrier, for instance on the bottom and/or the upper side of thecarrier.

In another preferred method of the present invention the carrier is athickening agent mentioned before and the method further comprises thestep of painting, spraying, printing on or partial coating of a surfaceof an item. This method opens up for many new commerciallyopportunities. Preferably, the carrier is a thickening agent (or sensorcomposition) being arranged to a surface of an item before the indicatoris arranged to one or more limited portions of the thickening agent (orsensor composition).

In a preferred embodiment of the invention the thickening agent issprayed direct on a pharmaceutical and/or nutritional additive,preferably in the form of a pill and/or a tablet.

In another preferred embodiment of the invention the thickening agent isprinted on at least one of a paper, a fibre, a card and/or a label.Further, the thickening agent is preferably partial coating of a surfaceof packaging.

In more preferred embodiment according to the invention the methodfurther comprises the step of pretreating, modifying, preferablyhydrophobing the actual surface of an item. This step facilitates themigration of the indicator within or at a surface layer of thethickening agent and not within the actual item.

In a preferred embodiment of the invention a method for providing asensor for indicating a cumulative time period of presence of an ambientrelative humidity by providing a carrier with an indicator a carrieraccording to the invention is dipped into a salt solution.Alternatively, the salt solution being sprayed on to the carrier. Oneadvantage with this methods is that they enables to get enoughabsorbent, salt solution, into the carrier.

In another preferred embodiment of the invention the salt solution ispre-heated. Further, the carrier includes an absorbent componentsubsequently being dried in warm air. After drying, the indicator ispreferable applied on one side of the carrier.

In one embodiment of the invention the carrier is further being windupon a roll. Alternatively, polyeten or a double adhesive tape is rolledin the roll at the same time. Thereby, problems with indicators beingtransferred to the upper side and/or to the lower side of the carrier isavoided. It is also possible that a doped carrier, or another of theabove-described carriers, may be adhesively joined with an adhesivelayer permitting water transport through at least one layer of thecarrier. This is achieved either by designing the adhesive layer so thatit in itself permits the moisture transport, or by making the space inbetween open by not covering the whole surface between the dye carrierand the salt carrier. The advantage of dividing the dye and carrier isthat the handling of the materials is simplified. The manufacture of thepresent sensor also gets more flexible as it lowers the storage and lesscomplicated equipment may be used for the manufacture.

Further, the sensor can be provided with a protection cover, preferablyof a liquid impervious material. The cover being pulled of duringactivation of the sensor. Thereby, the cover has an improved protectionuntil it has been pulled off.

In a preferred embodiment of the present invention the method furthercomprises the step of adding a water keeping compound to the carrier. Onadvantage using a water keeping compound is that the agitation ofgravitation, specially on sensors indicating at lower relative humidity,is decreased.

In a preferred embodiment of the invention a sensor for indicating acumulative time period of presence of an ambient relative humidity,comprises an indicator and a carrier and the indicator is located at oneor more limited portions of the carrier, the carrier allowing migrationof the indicator within the carrier, wherein the indicator causing anextension thereof by migrating from the one or more limited portionswhen the ambient relative humidity level exceeds a predetermined level.The extension by migration is detectable by a user and the cumulativetime period is related to the extension by migration and thecharacteristics of the indicator and the carrier. The sensor accordingto the present invention is for use in at least one of the processes ofmanufacturing, printing, packing, wrapping, storing, transportation andhandling of an item, namely, processes in which an item is, or may be,exposed to the ambient surroundings.

In a preferred embodiment of the invention the sensor is at least one ofa sensitive items humidity sensor, a food stuff humidity sensor, abuilding- or construction material humidity sensor, a pharmaceuticalhumidity sensor, an electronic equipment humidity incorporating at leastone of the characteristics of the sensor described above and preparedaccording to at least one of the previously mentioned processes. Onelarge advantage with the sensor according to the present invention isthat the sensor may be used in a very wide range of different businessareas. The sensor is easily used everywhere where there is a risk that acertain item is exposed to moisture. For instance, it is of interest toindicate the amount of moisture in boats, vehicles, buildings and/orhouses. Also, military materials, such as weapons, are sensitive tomoisture.

Further, it is of interest for suppliers of electronic equipment toindicate wherever the equipment, such as mobile phones, is exposed tohumidity under transportation and/or use. For example, it is importantfor suppliers or sellers to prove that a user has dropped his/hersmobile phone into water or the like.

In a preferred embodiment of the invention the sensor is provided withan additional component, namely a leakage-preventing barrier arranged tocover the surface layer of the sensor. The purpose of using a barrier isto protect the surroundings from leakage and above all the items onwhich the sensor is applied. This also protect the sensor from beingcontamined from the surroundings. Further, the leakage-preventingbarrier can be a membrane. In a preferred embodiment of the invention aleakage-preventing barrier is a semi-permeable membrane, permeable forwater vapour and/or steam, but not permeable to liquid water, in onedirection, i.e. into the sensor. In addition, the membrane may also be aprotection against minor mechanical damages. For instance the membranemay be made of EPTFE (expanded polytetraflouroethylene, more known underthe trademark Goretex).

In another preferred embodiment of the invention a sensor is sprayeddirectly on a actual item or at a packing including sensitive goods orobjects. One or more sensors may also be arranged in a container duringtransportation or storing of items who being sensitive for humidity,such as vegetable food, fruit foods and/or other provisions.

Definitions

As used herein the term thickening agent is interpreted to include aconsistency agent and/or a gel agent.

As used herein especially used in claim 1 the term within, means that aindicator according to the invention, located at one or more limitedportions of an carrier, is arranged to migrate in, at or on the carrier,preferably from the interior of the carrier to its surface and/or at asurface layer of the carrier.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and details of the present invention will become apparentfrom the following description when taken in conjugation with theaccompanying drawings, in which;

FIG. 1 a) shows one embodiment of a sensor according to one embodimentof the present invention and FIG. 1 b) illustrates how a cumulative timeperiod of presence of an ambient relative humidity being related to apredetermined humidity level and the extension by migrating of aindicator.

FIG. 2 shows a another embodiment of the sensor.

FIG. 3 shows a sensor exhibiting a circular shape having the migrationof a indicator towards the edges.

FIG. 4 shows a sensor according to the invention provided with a timescale.

FIG. 5 shows multiple sensors arranged on the same goods for differentintervals of relative humidity.

FIG. 6 shows an alterative embodiment of a sensor.

FIG. 7 shows yet another embodiment of a sensor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A number of preferred embodiments of a sensor for indicating acumulative time period of presence of an ambient relative humidity willbe disclosed below.

A first embodiment of a sensor for indicating a cumulative time periodof presence of an ambient relative humidity is presented in FIG. 1 a.The sensor 1 comprises a carrier 2 including an absorbent component 3and an indicator 4 being located at a portion of the carrier. Here, themain purpose of the carrier 2 is to provide a support material to keepthe components of the sensor assembled and to prevent convection oroccurrence of other undesired transport mechanisms. The absorbent 3 iscapable of absorbing water/water vapour from the surrounding air. Theabsorbent component 3 is designed to allow the indicator 4 to migratethrough and/or within said carrier 2 including an absorbent component 3in response to said ambient humidity and the indicator causing anextension by migrating from the one or more limited portions when theambient relative humidity level exceeds a predetermined level. When therelative humidity level is lowered below said predetermined relativehumidity level the migration of the indicator 4 ceases. The indicator 4resumes migration when the ambient relative humidity again exceeds saidpredetermined level. This procedure is repeated until the indicator 4has migrated through the whole carrier 2. FIG. 1 b) illustrates thecumulative time period of presence of an ambient relative humidity levelbeing related to the extension by migrating. In figure la it is assumedthat the sensor 1 is arranged to (an item in question. Preferably, thesensor has a bottom portion comprising a fastening means to allowattachment to an item being exposed to the ambient surroundings. In theembodiment as shown in FIG. 1, the sensor 1 has an essentiallyrectangular shape exhibiting a longitudinal migration direction x.Before activation, the indicator 4 is located at a limited portion 5 ofthe carrier 2. Upon exposure of a predetermined level of ambientrelative humidity, the indicator 4 migrates in the direction x of theabsorbent component 3 along the sensor in response to said ambienthumidity.

In a second embodiment of the invention the indicator 4 is arranged ontothe bottom portion of a carrier with hygroscopic characteristics. Thecarrier 2 can exhibit a wedge-shaped cross-section, as shown in FIG. 2,exhibiting a vertical migration direction z. In this embodiment, theindicator 4 migrates within the carrier preferably in the z direction,wherein the z direction is defined to be approximately upwards throughthe carrier 2 in response to said ambient humidity. As the indicator 4moves within the carrier 2 the exposure time can be estimated due to itswedge-shape, since it will take longer for the indicator 4 to migrate inone first end through the thicker layer of the carrier 2, than for theindicator 4 to migrate through the thinner layer of a second end.Further, it is also possible that the carrier includes an absorbentcomponent.

In a third embodiment of the invention shown in FIG. 3, the sensor 1 hasan essentially circular shape carrier 2, including an absorbentcomponent 3, exhibiting a surface layer area 7. Before activation, theindicator 4 is arranged preferably in the central part 8 of the carrier.The indicator causes an extension by migrating from the surface area 7towards the edges 9 of the carrier, when the ambient relative humiditylevel exceeds a predetermined level. The extension by migrating isdetectable by a user.

In a fourth embodiment of the invention the sensor comprising a carrierand an indicator for indicating of a cumulative time period of presenceof an ambient relative humidity. The carrier here is a thickening agent,such as a gel matrix, and being painting on, spraying, printing, andpartial coating of a surface of an item. Further, the indicator isarranged to one or more limited portions of the carrier. (Not shown.)

In a fifth embodiment, as shown in FIG. 4, the sensor may be providedwith a time axis 11 in order to determine the exposure time for acertain level of relative humidity. The sensor may be designed withseveral absorbent components 3 arranged to each other having differentrelative humidity equilibrium properties, i.e., the time axis 11 willthen indicate the respective exposure times for different levels ofrelative humidity as shown in FIG. 5.

The sensor according to the invention may be provided with a fourthcomponent, namely a leakage-preventing barrier 10 arranged to coverpreferably a outer surface of the sensor. The leakage-preventing barriermay be a membrane, such as a semi-permeable membrane.

The sensor may also exhibit a folded structure as shown in FIG. 6. Inthis embodiment the sensor is folded once and the indicator 4 isarranged in the bottom portion of the folded sensor. An imperviousmembrane 14 is arranged between the folded carrier portion 2, preferablyincluding the absorbent component 3. In this way the shift of theindicator 4 is delayed and the size of the sensor is decreased.

In a sixth embodiment, the sensor exhibits another folded spiral-shapedstructure as shown in FIG. 7. In this embodiment the sensor is foldedhaving the indicator 4 arranged in the core portion of the foldedsensor. An impervious membrane 15 is arranged on the wrapped carrier 2including the absorbent component 3. In this way the shift of theindicator 4 is delayed and the size of the sensor may be decreased.

A sensor according to the invention can also be provided with a “window”on the sensor in order to monitor a certain relative humidity interval.In this way it is possible to use the same sensor for differentapplications.

In a seventh embodiment of the invention a method for reading thecumulative time period of presence of an ambient relative humidityindicated by a sensor according to the invention comprises the steps of;observing the extension of the indicator having extended by migrationfrom one or more limited portions, when the ambient relative humiditylevel have exceeded a predetermined level; and establishing thecumulative time period of presence of an ambient relative humidity byrelating the extension of the indicator to a time period reference. Thetime period reference is one of; arranged in relation to the carrier, astand alone tool for physical alignment to the extension of the carrierat the time of the measuring of the extension and a table comprisingrelations between extension and time.

It should be understood that many modifications of the above embodimentsof the invention are possible within the scope of the invention such asthe latter is defined in the appended claims.

Experiment

The invention will now be closer illustrated by means of the followingnon-limiting examples. These examples are set forth merely forillustrative purposes and many other variations of the method may beused.

EXAMPLE 1

Preparation of Sensors

A glass fibre filter of the type MGA (Munktell) was used as carrier. Thesalt KCl (85% RH, quality p.a.) was used as absorbent component andquinoline yellow (BI04), caramine (E120) and patent blue (B131) (foodquality) respectively, were used as indicator dyes. The deionised waterused exhibited a quality of 18 M ohm/cm.

The carriers have been prepared in two different ways with the sameresults, either by dipping the carrier into a concentrated salt solution(KCl) or by spraying a salt solution on one side of the carrier. In thiscase the other side of the carrier was vented. The doped carrier is thendried to a stable weight. The indicator dye, which is dispersed inisopropanole, is applied on one side of the dried and doped carrier. Thesensor is then placed in a climate chamber having a relative humidity(RH) level lower than 55% RH.

Treatment of Sensors in a Climate Chamber

The test samples of the different sensors had a size of about 2 cm².Further, there were three of each type and a reference sample. The testsamples were placed in a pressure moisture chamber having an accuracyregarding the relative humidity level of about 0.5% RH and the desiredlevels of the relative humidity were set to the desired values. The testcourse was as follows: 75%, 75%, 80%, 83%, 86%, 89% and 50% RH. Themeasurements were performed on each level with a time period of at least24 hours between the observations. All the measurements were made at thetemperature of 20° C.

Changes in the Weight of the Sensors

The test samples were weighed on a balance a resolution of 0,001 g. Thesamples exhibited no weight change at 75%, 80% and 83% RH. At 86% RH,the test samples have increased their weight of about 0.05 g and anotherweight increase of 0.20 g. The initial weight of the test samples wereresumed at 50% RH. The difference in the weight and the weight changebetween the samples was not significant and could therefore beneglected. The weight increase is assumed to be water being absorbed bythe test samples, since it was the only parameter being changed duringthe test cycle.

Visual Observations

The test samples were visually observed in respect of their colour shiftand migration distance. The indicator dyes starting to migrate at acertain RH value for all sensors having different indicator dyes appliedon them. In the case of quinoline yellow (EI04) it occurred at a RHvalue exceeding the equilibrium for the salt in the carrier at 86% RH.Caramine (EI20) was somewhat a head in this test at 80% RF and in thecase of patent blue (EI31) the shift occurred essentially before theestimated value, i.e., at the first level of the cycle, that is 75% RH.

The indicator migrates about 8-10 mm in the first 24 hours and then itwill take the indicator about 72-130 hours to migrate 20 mm. This istrue for all three indicator dyes. The front line of the migration ofthe indicator-dye is very clear and is easily seen by the naked eye.

As is evident from example 1, the EI04 without modifications turned outto be not good enough for use in a sensor according to the invention,whereas caramine and patent blue exhibited excellent properties, such asclear and significant shifts.

The example proves that the technology works by allowing transport of awater-soluble dye in a saturated salt solution, absorbed in theabsorbent component of the sensor, as a response to ambient relativehumidity levels. The test also proves that it is possible to accumulatethe exposure to moisture during a period of time.

Combinations of different kinds of carriers, salts and indicator dyeswill lead to the optimal sensor for the desired purpose regarding use,temperature and moisture content and falls in to the scope of theinvention. Further, for the same reasons using a sensor comprising acarrier with hygroscopic properties and a carrier will allow migrationof the indicator within the carrier when a ambient relative humiditylevel is exceeding a predetermined humidity level and an accumulativetime period being related to the extension by migration and thecharacteristics of the indicator and the used carrier.

The invention shall therefore not be limited to the above shownembodiments and examples, but shall be interpreted within the scope ofthe appending claims. TABLE 1 E400-E495 E  400 Alginic acid E  401Sodium alginate E  402 Potasssium alginate E  403 Ammonium alginate E 404 Calcium alginate E  406 Agar E  407 Carrageenan E  407a ProcessedEuchema Seaweed E  410 Locust bean gum E  412 Guar gum E  413 TragacanthE  414 Acacia gum (Gum arabic) E  415 Xanthan gum E  417 Tara gum E  418Gellan gum E  422 Glycerol E  440 Pectins, Amidated pectin E  460Microcrystalline cellulose, Powdered cellulose E  461 Methyl cellulose E 463 Hydroxypropyl cellulose E  464 Hydroxypropyl methyl cellulose E 465 Ethyl methyl cellulose, Ethyl hydroxyethyl cellulose E  466 Carboxymethyl cellulose, Sodium carboxy methyl cellulose E  469 Enzymaticallyhydrolysed carboxymethylcellulose E  470a Sodium, potassium and calciumsalts of fatty acids E  470b Magnesium salts of fatty acids E  471 Mono-and diglycerides of fatty acids E  472a Acetic acid esters of mono- anddiglycerides of fatty acids E  472b Lactic acid esters of mono- anddiglycerides of fatty acids E  472c Citric acid esters of mono- anddiglycerides of fatty acids E  472d Tartaric acid esters of mono- anddiglycerides of fatty acids E  472e Mono- and diacetyl tartaric acidesters of mono- and diglyc- erides of fatty acids E  472f Mixed aceticand tartaric acid esters of mono- and diglyc- erides E1404-E1451 E 1404Oxidized starch E 1410 Monostarch phosphate E 1412 Distarch phosphate E1413 Phosphated distarch phosphate E 1414 Acetylated distarch phosphateE 1420 Acetylated starch E 1422 Acetylated distarch adipate E 1440Hydroxy propyl starch E 1442 Hydroxy propyl distarch phosphate E 1450Starch sodium octenyl succinate E 1451 Acetylated oxidised starch

1. Sensor for indicating a cumulative time period of presence of anambient relative humidity, the sensor comprising an indicator and acarrier, the indicator and the carrier being humid at approximately thesame time, the indicator being located at one or more limited portionsof the carrier; the carrier allowing migration of the indicator withinthe carrier; the indicator causing an extension thereof by migratingfrom the one or more limited portions when the ambient relative humiditylevel exceeds a predetermined level; the extension by migrating beingdetectable by a user; and the cumulative time period being related tothe extension by migration and the characteristics of the indicator andthe carrier.
 2. Sensor according to claim 1, wherein the carrier is ahygroscopic material.
 3. Sensor according to claim 2, wherein thehygroscopic material is one of an absorbent and a suitable porousmaterial.
 4. Sensor according to claim 2, wherein the hygroscopicmaterial is a hygroscopic thickening agent.
 5. Sensor according to claim4, wherein the hygroscopic thickening agent is one of a gel compound, agel matrix and gelatine.
 6. Sensor according to claim 3, wherein theabsorbent is a salt.
 7. Sensor according to claim 1, wherein the carrierfurther comprises a hygroscopic thickening agent for keeping water inthe carrier.
 8. Sensor according to claim 3, wherein the suitable porousmaterial has a continues pore system and is one of fibre, paper, wood,corrugated fibreboard, woven materials and clay.
 9. Sensor according toclaim 1, wherein the indicator is a colour indicator such as dye,pigment, hue and paint.
 10. Sensor according to claim 9, wherein thecolour of the indicator is visible to a user before use of the sensor;and the colour of the indicator still is visible until a predeterminedcumulative time period of presence of an ambient relative humidity isexceeded.
 11. Sensor according to claim 1, wherein the carrier isarranged to allow migration of the indicator from the interior of thecarrier to its surface, allowing visual detection of a user.
 12. Sensoraccording to claim 1, wherein the carrier is arranged to allow migrationof the indicator at a surface layer of the carrier, allowing visualdetection of a user.
 13. Sensor according to claim 1, wherein theextension by migration of the indicator is related to a colour shift ofa non-migrating indicator located at one or more limited portions on thecarrier.
 14. Method for reading the cumulative time period of presenceof an ambient relative humidity indicated by a sensor according to claim1, comprising the steps of: observing the extension of the indicatorhaving extended by migrating from one or more limited portions when theambient relative humidity level have exceeded a predetermined level; andestablishing the cumulative time period of presence of an ambientrelative humidity by relating the extension of the indicator to a timeperiod reference.
 15. Method according to claim 14, wherein the timeperiod reference is one of arranged in relation to the carrier; a standalone tool for physical alignment to the extension of the carrier at thetime of the measuring of the extension; and a table comprising relationsbetween extension and time.
 16. Method according to claim 14, wherein anexternal light source is used to assist in the visual detection. 17.Method according to claim 16, wherein the light source is one of aninfra-red light source, an ultra violet light source and a visiblemonochrome light source.
 18. Method for providing a sensor forindicating a cumulative time period of presence of an ambient relativehumidity by providing a carrier with an indicator, the indicator beingarranged to one or more limited portions of the carrier, the indicatorand the carrier being humid at approximately the same time.
 19. Methodaccording to claim 18, wherein the carrier is a thickening agent andfurther comprises the step of painting, spraying, printing on, orpartial coating of a surface of an item.
 20. Method according to claim19, further comprising the step of hydrophobing the surface.
 21. Methodaccording to claim 18, wherein the carrier is dipped into a saltsolution.
 22. Method according to claim 18, wherein a salt solution issprayed on the carrier.
 23. Method according to at least one of claim 18and 19, further comprising the step of adding a water keeping compoundto the carrier.
 24. A sensor according to claim 1 for use in theprocesses of manufacturing, printing, packing, wrapping, storing,transportation and handling.
 25. Sensitive items humidity sensorincorporating the sensor according to claim
 1. 26. Food stuff humiditysensor incorporating the sensor according to claim
 1. 27. Buildingmaterial humidity sensor incorporating the sensor according to claim 1.28. Pharmaceutical humidity sensor incorporating the sensor according toclaim
 1. 29. Electronic equipment humidity sensor incorporating thesensor according to claim 1.